1. Field of the Invention
The present invention relates to a Group III nitride-based compound semiconductor light-emitting device having a quantum well structure.
The invention also relates to a method for producing a Group III nitride-based compound semiconductor device or light-emitting device, and more particularly, to a method for growing an indium-containing Group III nitride-based compound semiconductor layer.
2. Description of the Related Art
Conventionally, Group III nitride-based compound semiconductor light-emitting devices employ a multiple quantum well (MQW) structure in which layers having different bandgap energies are alternatingly stacked at a predetermined number of repetitions of a stacked layer cycle. Examples include a blue-light-emitting diode (LED) and a green-light-emitting LED, employing a multiple quantum well (MQW) structure in which well layers In0.2Ga0.8N (thickness: 2.5 nm) and barrier layers (thickness: 5 nm) formed of In0.05Ga0.95N or GaN are alternatingly stacked. Other examples include a blue-light-emitting diode (LED) and a green-light-emitting LED, employing a single quantum well (SQW) structure having a single well layer (thickness: about 3 nm) Recently, near-UV-light-emitting LEDs (emission wavelength: about 380 nm) and laser diodes (LD) emitting a blue-purple light (405 nm) have been proposed. These proposed devices have a structure in which an InGaN well layer is interposed between AlGaN barrier layers.
Generally, when a heterojunction structure selected from the above structures has defects caused by lattice mismatch at a heterojunction interface, a light-emitting device employing such a heterojunction exhibits decreased light intensity and output as well as shortened service life due to deterioration, which are problematic. Characteristics of semiconductor per se also cause problems, since, as shown in FIG. 1, Group III nitride-based compound semiconductors have different lattice constants in accordance with the element compositions and compositional proportions. Among these problems, dislocation occurs in recent LEDs emitting near-UV light (about 380 nm) and LDs emitting a blue-purple light (405 nm) employing an AlGaN barrier layer.
Japanese Patent Application Laid-Open (kokai) Nos. 64-17484, 11-26812, and 2001-230447 disclose means for solving the aforementioned problems related to lattice mismatch in Group III nitride-based compound semiconductor light-emitting devices.
Meanwhile, an indium-containing Group III nitride-based compound semiconductor layer is employed as a narrowest-bandgap layer in a Group III nitride-based compound semiconductor light-emitting device exhibiting a wide bandgap. For example, an indium-containing Group III nitride-based compound semiconductor layer is an important layer for serving as a light-emitting layer in a light-emitting device. When the indium-containing Group III nitride-based compound semiconductor layer is interposed between aluminum-containing Group III nitride-based compound semiconductor layers, mutual diffusion of indium and aluminum is known to occur. The diffusion is conceived to be caused by thermal diffusion occurring in the growth layer during epitaxial growth, a so-called memory effect of the reaction system in a production apparatus, and migration as contaminants. These features are disclosed in Japanese Patent Application Laid-Open (kokai) Nos. 10-107319, 2000-340839, and 2004-253819